Tapping screw and fastening structure using the same

Abstract

To provide a tapping screw that is easy to fasten and difficult to loosen, and a fastening structure using the same. 【Means for solving the problem】 A pair of tapping screws 10 having a first thread portion 13 and a second thread portion 14, and screwed into a counterbore 21 of a mating member 20 for fastening, wherein the outer diameter of the second thread portion is equal to or less than the inner diameter of the counterbore of the mating member.

Description

Technical Field

[0001] The present invention is a tapping screw used for attaching parts of precision instruments such as automobiles, home appliances, electronic device parts, office equipment such as copiers, and optical instruments such as digital cameras, and mobile phones.

Background Art

[0002] Conventionally, as a tapping screw, particularly for use with materials such as soft metals and synthetic resin materials, there is, for example, a multi-threaded screw for preventing loosening (see Patent Document 1). When the multi-threaded screw for preventing loosening is screwed into the mounting hole 11 of the member to be mounted 10, the first thread portion 1 and the second thread portion 2 cut spiral grooves (female threads) on the inner peripheral surface of the mounting hole 11, respectively, and then penetrate into the mounting hole 11 of the member to be mounted 10 to complete the fastening.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as is clear from FIGS. 3 and 4 of Patent Document 1, a part of the member to be mounted 10 pushed out from the inner peripheral surface of the mounting hole 11 of the member to be mounted 10 is not sufficiently filled in the valley portion formed between the first thread portion 1 and the second thread portion 2. For this reason, a large gap is generated between the member to be mounted 10 and the multi-threaded screw for preventing loosening. As a result, a sufficient contact area cannot be obtained between the multi-threaded screw for preventing loosening and the member to be mounted 10, so that a sufficient anchor effect cannot be obtained and a desired loosening prevention effect cannot be obtained. In view of the above problems, an object of the present invention is to provide a tapping screw that is easy to fasten and difficult to loosen, and a fastening structure using the same.

Means for Solving the Problem

[0005] The tapping screw according to the present invention is, in order to solve the above problem, a tapping screw having a first thread portion and a second thread portion, and being a pair of two tapping screws that are screwed into a counterbore of a mating member and fastened, wherein the first thread portion is circular in an axial view, the second thread portion is circular in an axial view, and an outer diameter of the second thread portion is equal to or smaller than an inner diameter of the counterbore of the mating member together with the outer diameter dimension of the second thread portion is 73% to 83% of the outer diameter dimension of the first thread portion, and among the gaps formed between the groove portion located between adjacent first thread portions and the inner peripheral surface of the counterbore of the mating member, 65% or more of the said gaps are buried by a part of the mating member extruded onto the first thread portion configured as such.

Effect of the Invention

[0006] According to the present invention, a part of the mating member extruded to the first thread portion is filled in a valley portion formed between the first thread portion and the second thread portion and contacts the second thread portion. Therefore, the contact area between the support member and the tapping screw increases, and the frictional force increases, thereby obtaining an effect of being difficult to loosen. According to the present invention, when a part of the mating member comes into contact with the second thread portion, there is an effect that the contact area increases, the frictional force increases, and loosening is less likely to occur

[0007] As an embodiment of the present invention, the flank surface of the first thread portion may be bent in two steps. According to this embodiment, when the mating member is, for example, a resin material, the flow of the resin material is improved, the base portion of the first thread portion becomes thick, it becomes difficult to twist, and the mechanical strength is improved.

[0008] As another embodiment of the present invention, a fine groove may be provided along the top of the second thread portion. According to this embodiment, the surface area of the second thread portion increases, and the contact area with a part of the mating member increases, so that the frictional force increases and the tapping screw becomes difficult to loosen.

[0009] As another embodiment of the present invention, a part of the mating member extruded to the first thread portion may enter between adjacent first thread portions and be filled so as to contact the second thread portion.

[0010] According to this embodiment, a part of the mating material that has intruded between adjacent first thread portions comes into contact with the second thread portion, increasing the frictional force and making the tapping screw less likely to loosen.

[0011] The fastening structure of the tapping screw according to the present invention is configured to fasten the member to be fastened to the mating material by screwing the aforementioned tapping screw into the counterbore of the mating material.

[0012] According to the present invention, a part of the mating material pushed out by the first thread portion fills the valley portion formed between the first thread portion and the second thread portion and comes into contact with the second thread portion. For this reason, the contact area between the support member and the tapping screw increases, and the frictional force increases, resulting in the effect of being less likely to loosen.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0014] Embodiments of the tapping screw according to the present invention and a fastening structure using the same will be described with reference to the accompanying drawings in FIGS. 1 to 14. As shown in FIGS. 1 to 6, the tapping screw 10 according to the first embodiment includes a head portion 11 and a shaft portion 12, and is a double-threaded screw having a first thread portion 13 and a second thread portion 14 on the shaft portion 12.

[0015] The shape of the first thread portion 13 may be, for example, a substantially triangular shape having two-step inclined surfaces as shown in FIG. 6, in addition to a triangular cross-section, an equilateral triangular cross-section, and an isosceles triangular cross-section. The thread angle of the first thread portion 13 may be, for example, 30 to 50 degrees, preferably 45 degrees. If it is less than 30 degrees, the cross-sectional area of the first thread portion becomes thin and it is likely to break due to the shearing force generated during the fastening operation. If it exceeds 50 degrees, the pushing force against the mating member becomes too large and there is a risk of damaging the mating member. In particular, the angle of the base of the first thread portion 13 may be 70 to 120 degrees, preferably 90 degrees (see Fig. 6). If it is less than 70 degrees, the gap is likely to become large and it is difficult to obtain the desired contact area. If it exceeds 120 degrees, the resistance of the mating member becomes large, so a large fastening force is required during the fastening operation. Of course, the base of the first thread portion 13 does not have to be a straight line and may be a curve. This makes the flow of the extruded mating member smoother. Also, the pitch of the first thread portion 13 may be 30 to 45% of the nominal diameter, preferably 34 to 42%. If it is less than 30%, a sufficient cross-sectional area cannot be ensured for the female thread formed in the mating member and the female thread is likely to be damaged. If it exceeds 45%, it is difficult to obtain the desired fastening force and it is likely to loosen.

[0016] The shape of the second thread portion 14 may be the same as that of the first thread portion. For example, in addition to a triangular cross-section, it may be an equilateral triangle cross-section, an isosceles triangle cross-section, or a substantially triangular shape with two inclined surfaces. The thread angle of the second thread portion may be, for example, 30 to 90 degrees, preferably 45 degrees. If it is less than 30 degrees, the mechanical strength of the thread portion of the male thread becomes low and it is likely to break. If it exceeds 90 degrees, it becomes difficult for the second thread portion to contact the mating member, the desired contact area cannot be obtained, and the anti-loosening effect cannot be obtained. The outer diameter dimension of the second thread portion 14 is preferably equal to or less than the inner diameter of the counterbore of the mating member. If the outer diameter dimension of the second thread portion 14 exceeds the inner diameter of the counterbore of the mating member, the top of the second thread portion 14 will bite into the inner peripheral surface of the counterbore, increasing the screwing torque. And the outer diameter dimension of the second thread portion 14 may be 73% to 83%, preferably 76% to 80% of the outer diameter dimension of the first thread portion 13. If it is less than 73%, a part of the mating member extruded by the fastening operation of the first thread portion 13 will be less likely to contact the second thread portion 14, and it will be difficult to obtain the anti-loosening effect. Also, if it exceeds 83%, a part of the mating member will contact the second thread portion before the completion of the fastening operation, increasing the screwing torque and making the fastening operation difficult. In addition, the surface of the second thread portion 14 may be made into an uneven surface by blasting or the like to increase the surface area.

[0017] Regarding the shape and outer diameter dimension of the second thread portion 14, when the first thread portion 13 bites into the inner peripheral surface of the counterbore, it is preferable to design such that a part of the mating member 20 extruded by the first thread portion 13 fills the space formed between the first thread portion 13 and the second thread portion 14 and the inner peripheral surface of the counterbore. This is because the contact area between a part of the extruded mating member and the first thread portion 13 and the second thread portion 14 increases, increasing the frictional force and making it difficult to loosen. As a result, there is an advantage that a fastening structure that is less likely to loosen can be obtained with a fastening torque equivalent to that of a single tapping screw. More specifically, it is preferable that the volume of the portion extruded by the first thread portion 13 from the inner peripheral surface of the counterbore of the mating member is equal (100%) to 65% or more of the volume of the gap between the inner peripheral surface of the counterbore and the surface of the shaft portion 12. If it is less than 65%, a part of the extruded mating member will not sufficiently contact the second thread portion, the frictional force will be small, and the desired anti-loosening effect cannot be obtained. For this reason, for example, if it is a tapping screw with a nominal diameter of 4 mm, a diameter of the counterbore of the mating member made of a synthetic resin material of 3.25 mm ± 0.05 mm is appropriate.

[0018] The mating material is, for example, a synthetic resin material such as ABS resin, but is not limited to a synthetic resin material alone and may be a synthetic resin material to which a reinforcing material such as carbon fiber has been added.Furthermore, the mating material is not limited to a synthetic resin material and may be a soft metal material such as aluminum or copper.

[0019] The inner diameter of the pilot hole of the mating material is determined by the outer diameter of the tapping screw 10, the shape of the first thread portion 13, etc., but may be 70 to 90%, preferably 75 to 87%, of the nominal diameter of the tapping screw 10. If it is less than 70%, the roots of the tapping screw will come into contact with the inner peripheral surface of the pilot hole, requiring a large tightening force for the tightening operation, and if it exceeds 90%, the desired anti-loosening effect cannot be obtained.

[0020] 7 to 12, the second embodiment is substantially the same as the first embodiment described above, except that the cross-sectional shape of the second thread portion 14 is trapezoidal and a narrow groove 15 is formed along the apex of the second thread portion 14. The same parts are designated by the same numbers and their explanations will be omitted. The thread angle of the first thread portion 13 according to this embodiment is 45 degrees. The second thread portion 14 according to this embodiment has narrow grooves 15 formed by arranging threads with a thread angle of 45 degrees in parallel. The second thread portion 14 may be formed by arranging threads with a thread angle of 60 degrees in parallel to form the narrow grooves 15, as shown in Fig. 13. The second thread portion 14 may be formed by arranging threads with a thread angle of 90 degrees in parallel to form the narrow grooves 15, as shown in Fig. 14. Also, in the second embodiment, the first thread portion 13 may of course have a flank surface that is inclined in two steps, similar to the first embodiment.

[0021] Next, with reference to Figures 15 to 18, we will explain the various torques that occur when fastening the workpiece 25 by fastening the tapping screw 10 into the pilot hole 21, which is a through hole in the mating material 20, and the various torques that occur when loosening the fastened tapping screw 10. In this embodiment, the mating member 20 refers to a member into which the tapping screw 10 is directly screwed to form a female thread. The inner diameter of the lower hole refers to the diameter of the lower hole 21 formed in the mating member 20 to form the female thread. The member to be fastened 25 refers to the member clamped between the head 11 of the tapping screw 10 and the mating member 20. The driving torque TD refers to the maximum value of the torque required until the tapping screw 10 starts to form a female thread in the lower hole 21 of the mating member 20 and seats. Seating means that the head of the tapping screw contacts the member to be fastened. The breaking torque TB refers to the maximum torque generated until the female thread and / or male thread formed in the mating member 20 breaks. The tightening torque TT refers to the torque generated when the tapping screw 10 is screwed in. The proper tightening torque refers to the optimal tightening torque calculated from the results of the screwing test, and as an example, it is obtained by the following formula. Proper tightening torque = TDmax + (TBmin - TDmax) × 0.5 The loosening torque TL refers to the maximum torque required to loosen the tapping screw 10 after tightening with a predetermined tightening torque. The torque ratio refers to the minimum value of the breaking torque / the maximum value of the driving torque (= TBmin / TDmax). When the torque ratio is large, the torque setting range of the electric driver can be set wide, making the work easier. Practically, the torque ratio is preferably 2.5 times or more. The loosening rate refers to (TL / TT) × 100, where TL is the loosening torque and TT is the tightening torque. The thrust refers to the force that pushes the tapping screw 10 in the axial direction when fastening the tapping screw 10. The clamp force CL refers to the force that tightens the member to be fastened 25 when the tapping screw 10 extended in the axial direction tries to contract. The breaking axial force (breaking CL) refers to the axial force when the male thread and / or female thread is broken. <()

[0022] In addition, as shown in FIGS. 19 to 22, regarding the various torques generated when fastening the tapping screw 10 to the lower hole 21, which is the bag hole of the mating member 20, to fasten the member to be fastened 25, and the various torques generated when loosening the fastened tapping screw 10, since it is the same as the case of fastening a tapping screw to the lower hole 21, which is a through hole, the same characters are assigned to the same torque and the description is omitted.

[0023] As described above, various embodiments have been described in detail with reference to the drawings. Hereinafter, various aspects according to the present invention will be described. In the following description, as an example, reference numerals are also provided.

[0024] The tapping screw 10 according to the first aspect of the present invention is It includes a first thread portion 13 and a second thread portion 14, and is a pair of tapping screws 10 that are screwed into and fastened to the lower hole 21 of the mating member 20, The outer diameter of the second thread portion 14 is configured to be equal to or less than the inner diameter of the lower hole 21 of the mating member 20.

[0025] The tapping screw 10 according to the second aspect of the present invention has a configuration in which, in the tapping screw 10 of the first aspect, the flank surface of the first thread portion 13 is bent in two steps.

[0026] The tapping screw 10 according to the third aspect of the present invention is the tapping screw 10 described in the first aspect or the second aspect, A fine groove 15 is provided along the top of the second thread portion 14.

[0027] The tapping screw 10 according to the fourth aspect of the present invention is the tapping screw 10 described in any one of the first aspect to the third aspect, A part of the mating member 20 extruded by the first thread portion 13 enters between adjacent first thread portions 13, 13 and is filled so as to contact the second thread portion 14.

[0028] The tapping screw 10 according to the fifth aspect of the present invention is the tapping screw 10 described in any one of the first aspect to the fourth aspect, Of the gaps formed between the valley portions located between adjacent first thread portions 13, 13 and the inner peripheral surface of the counterbore 21 of the mating member 20, 65% or more of the gaps are buried by a part of the mating member 20 extruded onto the first thread portion 13.

[0029] The fastening structure of the tapping screw 10 according to the sixth aspect of the present invention is configured such that the tapping screw 10 described in any one of the first aspect to the fifth aspect is screwed into the counterbore 21 of the mating member 20 to fasten the fastened member 25 to the mating member 20.

Example

[0030] Taking the tapping screw according to Example 1 shown in Fig. 23 as a sample, various torques were measured using the measuring device shown in Fig. 24. As the tapping screw of Example 1, samples (3 in total) with a nominal diameter of 4 mm, an effective length of 25 mm, and a pitch of 1.46 mm having a binding head were used. More specifically, the outer diameter of the first thread portion was 4.1 mm, the valley diameter was 2.8 mm, the length below the head was 25.3 mm, the thread angle of the first thread portion was 45 degrees, and the height dimension of the entire first thread portion was 0.6 mm. However, the angle at the base from the valley portion of the first thread portion to one-third of the height was 90 degrees. The outer diameter of the second thread portion was 3.2 mm, the angle of the second thread portion was 45 degrees, and the height dimension was 0.2 mm. The sample was treated with trivalent chromate after zinc plating.

[0031] For the mating member 20, an ABS resin with a thickness of 25 mm provided with a counterbore having a diameter of 3.2 mm was used. A chamfer of 0.4 mm was provided at the opening edge of the counterbore. For the fastened member 25, a cold-rolled steel sheet (SPCC) with a thickness of 1.2 mm provided with a through hole having a diameter of 4.6 mm was used.

[0032] As the load sensor constituting the measuring device, a load cell 30 for M4 (manufactured by Kyowa Electronic Instruments Co., Ltd.) with a thickness of 8 mm and a maximum load of 10 kN was used. By appropriately using eight washers with a thickness of 1 mm and two washers with a thickness of 0.8 mm as the hanging adjustment materials, the threaded engagement length of the effective thread was adjusted to 8 mm. As the testing machine, an electric driver (manufactured by Atlascopco, ETD-ST-10-10) with an adjustable tightening torque, not shown in the figure, having a torque sensor of 10 Nm, a tightening rotation speed of 300 rpm, and a thrust of 30 N was used to conduct the screwing test and the loosening test.

[0033] Above the counterbore of the mating member 20, a plurality of washers, a load cell, a plurality of washers, and the fastened member 25 were stacked. Then, the tapping screws of the samples (three in total) were screwed into the mating member 20 via an electric nut runner, and the screwing torque TD, the tightening break torque TB, and the break axial force CL were measured. The measurement results are shown in Fig. 25. Note that all the breaks occurred in the female threads.

[0034] Also, the samples (three in total) were tightened with an electric driver adjusted to the proper tightening torque, and the tightening torque TT and the fastening axial force CL were measured. Then, the loosening torque TL was measured by loosening the fastened tapping screws with a testing machine. The measurement results are shown in Fig. 26.

[0035] Furthermore, with the tapping screws fastened to the mating member 20, the cross-section of the fastened state was photographed by cutting. The photographing results are shown in Fig. 27.

[0036] Next, based on Fig. 28, which is a partial enlargement of the photograph in Fig. 27, the voids remaining around the second thread portion were measured. The measured area was 0.0309 mm 2 It was. Based on the same photograph, the voids between the inner peripheral surface of the counterbore (indicated by the vertical line in Fig. 29) and the shaft portion were measured. The measured area was 0.1395 mm 2 It was. From this result, the filling rate of the voids by a part of the mating member extruded by the first thread portion was 77.8%. Comparative Example 1

[0037] As a sample of Comparative Example 1, tapping screws with a pitch of 1.46 mm were used as samples (a total of 3 pieces), which were manufactured in the same manner as in Example 1 except that the second thread portion provided in the sample of Example 1 was not formed. The same screwing test and loosening test as in Example 1 were conducted for measurement. The measurement results are shown in FIGS. 25 and 26, respectively. All the fractures occurred in the female screw.

[0038] Furthermore, with the tapping screw fastened to the mating member 20, the cross-section in the fastened state was photographed by cutting. The photographing result is illustrated in FIG. 30.

[0039] Next, based on FIG. 31 which is a partially enlarged view of the photograph in FIG. 30, the void remaining around the second thread portion was measured. The measured area was 0.0846 mm 2 It was. Based on the same photograph, the void between the inner peripheral surface of the pilot hole and the shaft portion was measured. The measured area was 0.1942 mm 2 It was. From this result, it was found that the filling rate with respect to the void formed by a part of the mating member extruded by the first thread portion was 56.4%. From this result, it was found that Example 1 had a larger filling rate and a larger contact area between the mating member and the shaft portion.

[0040] As is apparent from FIG. 25, it was found that Example 1 always had a larger breaking axial force and a larger torque ratio than Comparative Example 1. In particular, since the female screw of Example 1 was less likely to break, it was found that the axial force of Example 1, particularly the mechanical strength of the female screw, was high. Also, it was found that Example 1 could set a wider adjustment range of the electric driver than Comparative Example 1 and was easier to use.

[0041] As is apparent from FIG. 26, it was found that Example 1 had a larger loosening rate than that of Comparative Example 1 and was less likely to loosen.

[0042] In FIGS. 28 and 29 showing Example 1, a part of the mating member 20 extruded by the first thread portion 13 is in contact with the second thread portion 14. On the other hand, it can be seen that in FIGS. 31 and 32 showing Comparative Example 1 as well, a part of the mating member 20 extruded into the first thread portion 13 has moved between the first thread portion 13 and the first thread portion 13. However, it was found that a larger gap remained in the groove between the first thread portion 13 and the first thread portion 13 than in Example 1, and the same contact area as in Example 1 could not be obtained.

Example

[0043] The same tapping screw as used in Example 1 was used as a sample (a total of 3 pieces). Then, except for applying a lubricant to each sample, the test was conducted in the same manner as in Example 1 described above. As the mating member, as shown in FIG. 33, an aluminum plate (A5052) with a thickness of 3.0 mm provided with a pilot hole having a diameter of 3.2 mm substantially equivalent to the outer diameter of the second thread portion 14 of the tapping screw was used. As the fastened member, a cold-rolled steel sheet (SPCC) with a thickness of 1.2 mm provided with a pilot hole having a diameter of 4.6 mm was used.

[0044] For the sample of Example 2 as well, a screwing test and a loosening test were conducted in the same manner as in Example 1. The measurement results are shown in FIGS. 34 and 35 respectively. Note that all the fractures occurred in the female thread.

[0045] Similar to Example 1, for Example 2 as well, with the mating member cut in the fastened state, a cross-section of the fastened state was photographed. The photographing result is shown in FIG. 36. Comparative Example 2

[0046] As the sample of Comparative Example 2, tapping screws manufactured in the same manner as in Example 2 were used as samples (a total of 3 pieces), except that the second thread portion provided in the sample of Example 2 was not formed. Then, in the same manner as in Example 2, a screwing test and a loosening test were conducted. The test results are shown in FIGS. 34 and 35. Note that all the fractures occurred in the female thread.

[0047] Similar to Example 2, a photograph of the cross-section in the fastened state of Comparative Example 2 was taken. The photographing results are shown in Fig. 37.

[0048] As is clear from Fig. 34 showing the results of the screwing test, by comparing Example 2 and Comparative Example 2, the screwing torque TD of Example 2 is almost equivalent to the screwing torque TD of Comparative Example 2. Furthermore, the tightening breakage torque TB of Example 2 is almost equivalent to the tightening breakage torque TB of Comparative Example 2. And it was found that Example 2 has a larger torque ratio than Comparative Example 2. For this reason, it was found that Example 2 can set a wider setting range of the electric driver than Comparative Example 2 and is easier to use. As a result, it was found that the appropriate tightening torques of Example 2 and Comparative Example 2 are almost equivalent.

[0049] As is clear from Fig. 35 showing the results of the loosening test, the loosening rate of Example 2 is larger than the loosening rate of Comparative Example 2, and it was found that Example 2 is less likely to loosen than Comparative Example 2.

[0050] According to Fig. 36 showing Example 2, as the first thread portion 13 bites into the inner peripheral surface of the mating member 20, a part of the extruded mating member 20 intrudes between the first thread portions 13, 13 and contacts the second thread portion 14, and it was found that the contact area is large. On the other hand, also in Fig. 37 showing Comparative Example 2, it can be seen that a part of the extruded mating member 20 intrudes between the first thread portions 13, 13 as the first thread portion 13 bites into the inner peripheral surface of the mating member 20. However, it was found that a larger gap remains in Comparative Example 2 than in Example 2 and the same contact area as in Example 2 cannot be obtained. Therefore, even when the mating member 20 is an aluminum plate, it was found that Example 2 is not only as easy to fasten as Comparative Example 2, but also Example 2 is less likely to loosen than Comparative Example 2.

Example

[0051] Using three tapping screws identical to the tapping screw according to Example 1 shown in Fig. 23 as samples, various torques were measured using the measuring device shown in Fig. 24. More specifically, the outer diameter of the first thread portion was 4.06 mm, the root diameter was 2.82 mm, the length under the head was 25.3 mm, the thread angle of the first thread portion was 45 degrees, and the overall height dimension of the first thread portion was 0.6 mm. However, the angle at the base from the root of the first thread portion to one-third of the height was 90 degrees. The outer diameter of the second thread portion was 3.19 mm, the angle of the second thread portion was 45 degrees, and the height dimension was 0.2 mm. In addition, the sample was treated with trivalent chromate after zinc plating. For the mating member 20, a glass fiber-reinforced PPS resin material with a thickness of 8 mm provided with a pilot hole having a diameter of 3.35 mm was used. For the fastened member 25, a cold-rolled steel sheet (SPCC) with a thickness of 1.6 mm provided with a through hole having a diameter of 4.6 mm was used. Otherwise, a screwing test was conducted in the same manner as in Example 1. The measurement results are shown in FIG. 38. In addition, all the fractures occurred in the female thread. Comparative Example 3

[0052] Comparative Example 3 was produced in the same manner as in Example 3 except that the outer diameter of the second thread portion was 3.48 mm, and a sample produced in the same manner as in Example 3 was used. Therefore, the top of the second thread portion directly bites into the inner peripheral surface of the pilot hole. A screwing test was conducted in the same manner as in Example 3. The measurement results are shown in FIG. 38. In addition, all the fractures occurred in the female thread.

[0053] From the measurement results in FIG. 38, it was found that the screwing torque TD was smaller in Example 3 where the second thread portion did not bite into the inner peripheral surface of the pilot hole than in Comparative Example 3, and Example 3 was easier to perform the fastening operation than Comparative Example 3.

[0054] From the above test results, even if the mating member is, for example, an ABS resin material, a glass fiber-reinforced PPS resin material, and an aluminum material, in all of Examples 1, 2, and 3, the outer diameter of the second thread portion is equal to or less than the inner diameter of the pilot hole of the mating member. Therefore, during the fastening operation, the top of the second thread portion does not contact the inner peripheral surface of the pilot hole, and a large fastening torque is not required during the fastening operation. On the other hand, after the fastening operation, it was found that a part of the mating material extruded into the first thread portion intruded between the adjacent first thread portions and contacted the first thread portion and the second thread portion, increasing the frictional force and making it difficult to loosen. As a result, it was found that a tapping screw that is easy to fasten and difficult to loosen can be obtained.

Industrial Applicability

[0055] The tapping screw according to the present invention can be applied not only to hard or soft synthetic resin materials, but also to soft metal materials containing aluminum and to inorganic materials.

Explanation of Reference Numerals

[0056] 10 Tapping screw 11 Head 12 Shaft portion 13 First thread portion 14 Second thread portion 15 Fine groove 20 Mating material 21 Pilot hole 25 Fastened member 26 Through hole 30 Load cell

Claims

1. Two tapping screws having a first thread portion and a second thread portion, and being screwed into a counterbore of a mating member for fastening, wherein the first thread portion is circular in an axial view, the second thread portion is circular in an axial view, and an outer diameter of the second thread portion is equal to or smaller than an inner diameter of the counterbore of the mating member, and an outer diameter dimension of the second thread portion is 73% to 83% of an outer diameter dimension of the first thread portion, and among voids formed between a valley portion located between adjacent first thread portions and an inner peripheral surface of the counterbore of the mating member, at least 65% of the voids are filled by a part of the mating member extruded to the first thread portion. The tapping screw is characterized by this.

2. The tapping screw according to claim 1, wherein a flank surface of the first thread portion is bent in two steps.

3. The tapping screw according to claim 1, wherein a fine groove is provided along a top of the second thread portion.

4. The tapping screw according to claim 1, wherein a part of the mating member extruded to the first thread portion intrudes between adjacent first thread portions and is filled so as to contact the second thread portion.

5. A fastening structure of a tapping screw, characterized in that a tapped member according to any one of claims 1 to 4 is screwed into a counterbore of a mating member to fasten a member to be fastened to the mating member.

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